Calculate the thermal effect and short-circuit current by practical calculation method and equivalent time method. What are the characteristics?
A: The practical calculation method of the current is a short-circuit steady-state current, while the equivalent time method is to calculate the current is the sub-transient current method.
3-7 How does electromotive power affect the operation of conductors and electrical equipment?
A: Electrical equipment under normal conditions causes the flow of relative small current through the conductor so corresponding the small power, and therefore its not easy for people to perceive. In the short circuit analysis, especially when the impact of short-circuit current flows, the electric power can reach a large value, when the current conductor and electrical equipment, mechanical strength is not enough to withstand these limitations it will produce deformation or damage. In order to prevent this phenomenon, we must study the impact of short-circuit current generated by the size and characteristics of electric power in order to choose the appropriate strength of the conductor and electrical equipment to ensure adequate dynamic stability. For this purpose short circuit current limitations methods are also used.
3-8 Three-phase parallel conductor in the three-phase short-circuit occurs when the maximum power in which phase, try to explain.
A: Three-phase equal conductor short circuit occurs when the three-phase short with each other and maximum electric power appears in the B phase, because the three-phase short circuit, B-phase inrush current will be the maximum.
3-9 What is the meaning of the dynamic stress factor of a conductor, and under what circumstances dynamic stress is considered?
A: The dynamic stress coefficient β is the dynamic stress of a conductor is the ratio of static stress and the conductor vibration, the conductor will have a dynamic internal stress. The dynamic stress for the consideration is generally used to amend the static calculation method. That is, the maximum electric power Fmax. The number of dynamic stress system β obtain the actual dynamic process of the maximum dynamic stress.
3-10 Why does the high current bus bar uses the phase-separated busbar? What is the role of the enclosure of the separate busbar?
A: The high current bus is divided by phase bus is due to:
1) high reliability, because the bus is placed in the shell, to prevent phase short circuit, and the shell multi-point grounding can protect the human body to contact the phase.
2) short-circuit busbar inter phase electric power greatly reduced risk of shock due to the shielding effect of the shell vortex, so that the magnetic field is kept within the shell and weakened and reduces the short-circuit current when the electric power has obvious effect;
3) shell external magnetic field shielding effect weakening can be better choice to improve the bus near the steel heating;
4) the installation and the maintenance workload is very small.
3-11 How can we reduce the heat of the steel structure near the high-current busbar?
A: To reduce the heating near high current bus following are measures:
1) To increase the distance between the steel structure and the conductor, so that magnetic field strength weakened, which can reduce the eddy current and hysteresis loss;
2) Disconnect the steel loop, and the installation of insulation pads to eliminate current circulation;
3) The use of electromagnetic shielding;
4) The use of phase-enclosed bus.
wiring should be able to flexibly adapt to normal. Design should also pay attention to its economy and cautiously adopting new technologies, new equipment, so that factory wiring remains feasible and advanced in nature.
wiring should be able to flexibly adapt to normal. Design should also pay attention to its economy and cautiously adopting new technologies, new equipment, so that factory wiring remains feasible and advanced in nature.
⑸ In the design of factory wiring, but also should plant power voltage level, the neutral grounding, plant power and its connection and factory wiring and other forms of power analysis and demonstration.
The voltage grade of the auxiliary power is determined by the technical and economic comparison according to the rated voltage of the generator, the voltage of the auxiliary motor, the auxiliary power supply network and the power supply network.
